These are the candidates vying for the 2020 Democratic presidential nomination

With an unpopular incumbent Republican in the White House, and no clear favourite for the Democratic nomination, the contest is wide open.

So far, nine serious (or semi-serious) candidates have either announced they are running or formed exploratory committees to lay groundwork for a campaign. More than a dozen other potential major candidates are mulling throwing their hats into the ring before the first caucus in Iowa in February of next year.

The field of candidates is set to make history for its diversity, with more women and visible minorities than in any contest before.

Running

CORY BOOKER

Mr. Booker shot to national fame as the cool-guy mayor of Newark, N.J., overseeing a renaissance of his city’s downtown and personally fielding requests for municipal services on social media. Look for him to trade heavily on this image in the primaries (his introductory campaign video shows him strolling around his neighbourhood, shouting “wassup?” to passersby.) But his mixed record in city politics could also cause trouble: Mr. Booker’s tenure has regularly been criticized for making mostly cosmetic changes to Newark that didn’t effectively deal with underlying problems of poverty and unemployment.

A senator since 2013, Mr. Booker is also an Ivy-League-trained lawyer who spent a few years working for non-profit social-justice groups. Standing 6’3” with a well-modulated baritone, Mr. Booker has a stage presence that should stand him in good stead once the long string of crowded campaign debates begin in the spring.

JULIAN CASTRO

A 44-year-old lawyer from San Antonio, Tex., Mr. Castro served as secretary of housing and urban development during President Barack Obama’s second term. Mr. Castro has promised to overhaul the U.S. immigration system to make it possible for all unauthorized immigrants to obtain citizenship, create a subsidized prekindergarten program similar to one he set up locally while serving as mayor of San Antonio and bring in universal health care. He has an identical twin brother, Congressman Joaquin Castro.

Youthful and Latino, Mr. Castro appeals to two core Democratic constituencies that the party has to do a better job of motivating to get to the polls. Highlighting immigration could also help him stand out in the crowded field. His challenge will be building a national political organization that can help him break into the top tier of candidates.

TULSI GABBARD

Ms. Gabbard was first elected to Hawaii’s legislature at the age of 21, and has spent the last six years in the U.S. House of Representatives. In between, she served in the National Guard, including a tour of duty in Iraq.

Ms. Gabbard’s challenge will be generating attention against higher-profile candidates. She has also drawn criticism for helping her father, a Hawaii state senator, run a campaign against same-sex marriage in the state in the 1990s and early 2000s, and making homophobic comments at the time. Ms. Gabbard issued an apology last week, saying her views on LGBTQ issues have completely changed since then.

KAMALA HARRIS

A centrist first-term senator and former California attorney-general, Ms. Harris was a career prosecutor before getting into politics. She also has a Canadian connection: Ms. Harris spent her adolescence in Montreal, where her mother was a professor at McGill. Ms. Harris graduated from Westmount High School, whose alumni include Leonard Cohen and Moshe Safdie. Not that she was particularly enthralled with the bohemian metropolis, at least at first. “I was 12 years old, and the thought of moving away from sunny California in February, in the middle of the school year, to a French-speaking foreign city covered in 12 feet of snow was distressing, to say the least,” she recounts in her autobiography.

Ms. Harris’s legal background has made her effective in the Senate. But it could also come back to haunt her campaign in a party whose base is clamouring for criminal justice reform. Despite being personally against the death penalty, for instance, Ms. Harris fought a court decision that ruled the statute unconstitutional. And she opposed efforts to oblige the attorney-general’s office to investigate instances of police killing people.

AMY KLOBUCHAR

Ms. Klobuchar has cultivated the “Minnesota nice” stereotype of her home state, projecting a folksy public persona and earning a reputation for bipartisan cooperation during her three terms in the Senate. She has been a skilled legislator, sponsoring more successful bills in the last Congress than any other senator.

The former prosecutor hails from the party’s moderate wing; she’s shied away from embracing single-payer healthcare, for instance. While this may be an asset in winning over independent voters, it could work against her with a Democratic base that has moved steadily left in recent years.

Also working against her: A parade of former staffers who say Ms. Klobuchar frequently berates her aides in private, throws papers around her office when she gets upset and makes her staff come to her house and wash her dishes.

BERNIE SANDERS

The rumpled Vermont grandfather gave Hillary Clinton a run for her money in 2016, campaigning as an ideological purist against establishment interests. With his famously messy hair and gravelly Brooklyn accent (he grew up in New York before decamping for the Green Mountain State in his 20s), the self-described socialist Senator rocketed from long-shot to serious competitor. This time around, he starts his campaign near the top of most polls.

It’s a testament to the strength of Mr. Sanders’ previous run that most of his pledges – universal health care, free university tuition, paid parental leave, tighter rules for banks and other large corporations – have moved from the margins of American politics to the mainstream of the Democratic Party. But Mr. Sanders may be a victim of his own success: With no shortage of candidates championing his policies, Democratic voters may give the aging hippie a miss in favour of someone younger. Mr. Sanders’ previous run also left a bad taste for some Democrats, not least because of the “Bernie bros” – overzealous and often belligerent male supporters of the Senator who took to flaming Clinton supporters on social media.

Mr. Sanders has spent most of his adult life in politics, with stints as mayor of Burlington, Vermont and in the House of Representatives before winning a Senate seat in 2007.

ELIZABETH WARREN

In her seven years representing Massachusetts in the Senate, the former law professor has established herself as a leader of her party’s left. Best known for championing tougher regulation of the country’s banks, she also backs universal healthcare, cheaper student loans and a “wealth tax” on the richest Americans. Ms. Warren opposes the overhauled NAFTA – or U.S.-Canada-Mexico Agreement – because she argues it does not do enough to stop American manufacturing leaving the country.

Her skill at delivering a populist message – particularly when railing against the excesses of the financial industry – has delivered her a loyal following in a party whose appetite for a more aggressive policy agenda appears to be growing. It also sets her on a collision course with her Senate colleague Bernie Sanders, who is running pretty much the exact same messaging, as the two battle to become the standard-bearer for the left.

Ms. Warren has also faced accusations of cultural appropriation for referring to herself as “Native American” and “Cherokee” despite having no affiliation with any Indigenous nation and being unable to identify any Indigenous ancestors. She only complicated matters last year by trying to use a DNA test to validate her claim.

Exploring

PETE BUTTIGIEG

The 37-year-old mayor of South Bend, Ind., is aiming to become the U.S.’s youngest-ever and first openly gay president. A former political staffer and consultant, Mr. Buttigieg is also a naval reservist who did a tour of duty in Afghanistan during his first term as mayor.

Mr. Buttigieg faces long odds, largely because of a lack of name recognition. But the unpredictable nature of the country’s presidential politics may give him reason to hope for a breakthrough – or at least boost his profile enough to be named vice-presidential running mate by the eventual nominee.

KIRSTEN GILLIBRAND

During her decade in the Senate, Ms. Gillibrand has become known for successfully pushing for the repeal of the “don’t ask, don’t tell” policy that prohibited LGBTQ people from serving openly in the military, fighting against sexual misconduct and calling for the abolition of Immigration and Customs Enforcement, the agency that deports undocumented immigrants.

Ms. Gillibrand could face a bumpy ride from the base for her positions on immigration and gun control while serving as a congresswoman for a conservative upstate New York district in the 2000s: She voted to cut federal funds to sanctuary cities and make it easier to hunt, for instance. Her work as a lawyer for tobacco company Philip Morris in the 1990s could also hamper her campaign.